1. Field of the Invention
The present invention is concerned with the field of expansion joint fire barriers. More particularly, it is concerned with a preferred expansion joint fire barrier including two sheets of metal having rows of dimples defined in the respective surfaces thereof with a layer of fire resistant material between the sheets to form a fire barrier body presenting a concave configuration, and including a pair of attachment strips extending outwardly from opposed side edges of the barrier body.
2. Description of the Prior Art
One type of expansion joint fire barrier presents a layered construction composed of two sheets of stainless steel with fire resistant material therebetween forming a barrier body with attachment strips extending from side edges. Usually this type of barrier is longitudinally scored so that the barrier body can be formed into a concave configuration for placement into the gap of an expansion joint.
This type of fire barrier is normally manufactured in a planar configuration and then formed into a roll for shipment. On site, the barrier is unrolled and placed over the expansion joint gap. The barrier body is then formed into the concave configuration as defined by the score lines and placed in the gap. The attachment strips are then secured to the edges of the joint structure.
If smooth sheet metal is use to form the outer layers of the body, undesirable and randomly oriented creases develop in the sheet metal during formation into a roll and especially when it is unrolled on site. U.S. Pat. No. 5,032,447 discloses a fire barrier intended to solve this problem with corrugated outer sheet metal layers but, in so doing, presents problems of its own.
For example, corrugated material inherently requires an initial surface area greater than the final over all surface area of the barrier, which increases the cost of the barrier especially when high grade stainless steel is used. Additionally, the score lines are transverse to the corrugations which means that when the peaks of the corrugations are properly defined, the valleys are not scored properly. If the corrugations are deep enough to properly score the valleys, then the peaks can be weakened thereby adversely affecting the fire barrier integrity. More particularly, repeated bending cycles may induce failure at the corrugated score lines thereby preventing satisfaction of ASTM test D1399, which requires 5000 bending cycles without failure. These corrugations also present another problem because they increase the surface area of the barrier with a corresponding increase in the convective component of heat transfer, and increase the contact surface of the barrier resulting in an increased conductive component.